Vlasovite, Na2Zr(Si4O11), from the Kipawa alkaline complex, Quebec, Canada: crystal-structure refinement and polarized infrared spectroscopy

The crystal structure of vlasovite, Na-2 Zr (Si4O11), from the Kipawa alkaline complex, Quebec, Canada, monoclinic, a 11.0390(5), b 10.0980(3), c 8.5677(4) angstrom, beta 100.313(1)degrees, V 939.6(1) angstrom(3), space group 4,72/c. Z = 4, D (calc.) = 3.008 g.cm(-3), was refined to all R, index of 1.9% based oil 1352 observed [F-o > 4 sigma F] unique reflections measured with MoK alpha X-radiation on a Broker P4 diffractometer equipped with a 4K CCD detector. An electron-microprobe analysis gave the composition Na-1.98 Zr-1.00 (Si4O11) based on 11 O apfit. In the crystal structure, there ire two tetrahedrally coordinated Si sites with a grand < Si-O > distance of 1.612 angstrom, and one octahedrally coordinated Zr site with < Zr-O > = 2.085 angstrom. There are two Na sites: the Na(1) site is [7]-coordinated with < Na(1)-O > = 2.620 angstrom, The Na(2) site is split into two subsites, Na(2A) and Na(2B), with a separation of 0.829 angstrom, and the symmetry-related Na(2B) sites are separated by 1.525 angstrom. Na(2A) is octahedrally coordinated, and No(2B) is [5]-coordinated, and their occupancies are 0.826(8) and 0.092(4) Na, respectively. Thus the Na(1) and aggregate Na(2) sites are each fully Occupied. In the crystal structure of vlasovite, four-membered rings of (SiO4) tetrahedra link together to form an [Si4O11](6-) chain. Chains of tetrahedra and Zr octahedra link together to form a heteropolyhedral framework with channels extending along [001]. Three channels contain the Na atoms, which are bonded to O atoms of the octahedron-tetrahedron framework. Vlasovite is not significantly damaged by exposure to X-rays. Infrared spectro;copy shows that vlasovite can be free of H2O or can contain variable amounts of H2O; single crystals can be anhydrous in so ne regions and hydrous in other regions. Moreover, the H2O content and its spectral response are unaffected by exposure of crystals to X-rays.